In the manufacture of, for example, a lithium secondary battery, sequential coating in which one side of a raw material such as aluminum foil is coated with a coating liquid such as an electrolyte or the like at a time is performed. In the sequential coating, the side to be coated and the other side are held by a backup roller when a raw material is delivered and only one side is coated and dried and then, the other side is coated.
On the other hand, a double-sided coating apparatus that attempts to improve throughput by coating both sides at the same time is known. For example, a raw material is delivered in the horizontal direction to coat both sides of the raw material with a coating liquid. The raw material is directly carried into a drying oven without using a roller because if the roller comes into contact with a location coated with the coating liquid, the coating liquid adheres to the roller. In the drying oven, the raw material is floated by hot air blown strongly both from above and below to prevent the raw material from coming into contact with the oven. Such a drying oven is called a floating drying oven.
Such a double-sided coating apparatus has problems as follows: In an apparatus transporting a raw material in the horizontal direction, the raw material is not supported by a roller and thus, the position precision of the raw material is low, resulting in lower coating precision. Moreover, drying of the surface of the coating liquid is fast and cracks appear, leading to lower coating quality. Further, thermal conduction from the rear side of the coated surface is weak and the distribution of binder varies on the surface of the raw material or in the coating liquid, causing a problem of lower adhesion.
Also, an apparatus that coats both sides with a coating liquid at the same time by causing aluminum foil to proceed vertically upward and providing coating heads on both sides of the aluminum foil is proposed.
In such a double-sided coating apparatus, coating heads H capable of performing well-balanced coating on both sides at the same time are needed to hold the raw material vertically, leading to a possibility of higher equipment costs.
Further, the floating drying oven has a problem that a vibration is generated in the raw material by a hot air and the vibration is transmitted to a portion to be coated, thereby decreasing uniformity in thickness of a coating liquid. Further, tension cannot be individually set for a portion to be coated and a portion to be dried and therefore, it is difficult to make conditions for coating and drying effective.
An object of the present embodiment is to provide a double-sided coating apparatus capable of performing excellent double-sided simultaneous coating while using coating heads used for single-sided coating and a double-sided coating method.